This invention relates generally to expansion valves in refrigeration and air conditioning systems and in particular to an improved expansion valve which incorporates a reverse flow check valve.
Expansion valves are used in refrigerator and air conditioner systems as flow control devices which restrict the flow of liquid refrigerant as it passes from the condensor to the evaporator. Essentially, expansion valves control the flow of liquid refrigerant so that it arrives at the evaporator at a uniform rate consistent with the heat transfer capability of the evaporator coil.
Such expansion devices fall generally into two categories, namely fixed orifice devices and variable orifice valves. In addition, variable orifice valves themselves may be separated into two general classes namely automatic valves and thermostatic valves.
Thermostatic expansion valves are disclosed in U.S. Pat. No. 2,786,336 (H. T. Lange), U.S. Pat. No. 3,742,722 (Leimbach) and U.S. Pat. No. 3,738,573 (Eschbaugh). The first two of these three patents are assigned to the owner of the present invention. U.S. Pat. No. 2,786,336 is directed to providing an expansion valve which compensates for any increased pressure differential across the valve port, for any increased pressure unbalance of the valve port, and for any increased of suction temperature caused as the valve throttles, upon an,.degree. increase, of valve inlet or head pressure. U.S. Pat. No. 3,742,722 is directed to providing an expansion valve in which the valve member is pressure balanced by way of an orifice therethrough which communicates the inlet port with a chamber defined by the valve housing and valve member, the inlet pressure thus acting on equal areas on opposite sides of the valve member. Finally, U.S. Pat. No. 3,738,573 is directed to the provision of an expansion valve of pressure balanced construction for controlling flow in both large and small units.
In some refrigeration and air conditioning systems, and heat pumps represent a prime example, it is necessary to provide for reverse refrigerant flow in the system. If any of the known expansion valves, such as those discussed above, are used in the system it is necessary to provide parallel piping for an independent check valve in addition to the expansion valve. In the normal forward flow direction, the check valve closes and refrigerant flow is directed through the expansion valve. In the reverse flow direction, the check valve opens to allow refrigerant to by-pass the expansion valve.
Systems of this kind are not only cumbersome but tend to be expensive and the present invention solves this problem in a manner not disclosed in the known prior art.